Han Rim Lee

Development of array‐type prompt gamma measurement system for in vivo range verification in proton therapy

PURPOSE In vivo range verification is one of the most important parts of proton therapy to fully utilize its benefits delivering high radiation dose to tumor, while sparing the normal tissue with the so-called Bragg peak. Currently, however, range verification method is not used in clinics. The purpose of the present study is to optimize and evaluate the configuration of an array-type prompt gamma measurement system on determining distal dose edge for in vivo range verification of proton therapy. METHODS To effectively measure the prompt gammas against the background gammas, the Monte Carlo simulations with the MCNPX code were employed in optimizing the configuration of the measurement system, and the Monte Carlo method was also used to understand the effect of the background gammas, mainly neutron capture gammas, in the measured gamma distribution. To reduce the effect of the background gammas, the optimized energy window of 4-10 MeV in measuring the prompt gammas was employed. A parameterized source was used to maximize computation speed in the optimization study. A simplified test measurement system, using only one detector moving from one measurement location to the next, was constructed and applied to therapeutic proton beams of 80-220 MeV. For accurate determination of the distal dose edge, the sigmoidal curve-fitting method was applied to the measured distributions of the prompt gammas, and then, the location of the half-value between the maximum and minimum value in the curve-fitting was determined as the distal dose edge and compared with the beam range assessed by the proton dose distribution. RESULTS The parameterized source term employed in optimization process improved the calculation speed by up to ∼300 times. The optimization study indicates that an array-type measurement system with 3, 2, 2, and 150 mm for scintillator thickness, slit width, septal thickness, and slit length, respectively, can effectively measure the prompt gamma distributions minimizing the contribution of background gammas. The present results show that a few hundred counts of prompt gammas can be easily obtained by measuring 10 s at each measurement location for proton beams of ∼4 nA. The distal dose edges determined by the prompt gamma distribution are 5.45, 14.73, and 27.74 cm for proton beams of 5.17 (80 MeV), 14.99 (150 MeV), and 27.38 (220 MeV) cm, respectively. CONCLUSIONS The results show that the array-type measurement system can measure prompt gamma distributions from a therapeutic proton beam within a short measurement time, and that the distal dose edge can be determined within a few millimeters of error without using any sophisticated analysis.

Erratum: “Gamma electron vertex imaging and application to beam range verification in proton therapy” [Med. Phys.39(2), 1001–1005 (2012)]

Chan Hyeong Kim, Jin Hyung Park, Hee Seo, and Han Rim Lee Citation: Medical Physics 39, 6523 (2012); doi: 10.1118/1.4749930 View online: http://dx.doi.org/10.1118/1.4749930 View Table of Contents: http://scitation.aip.org/content/aapm/journal/medphys/39/10?ver=pdfcov Published by the American Association of Physicists in Medicine Articles you may be interested in Erratum: “Dynamically accumulated dose and 4D accumulated dose for moving tumors” [Med. Phys.39(12),7359–7367 (2012)] Med. Phys. 40, 047201 (2013); 10.1118/1.4794486 Response to “Comment on ‘It is not appropriate to “deform” dose along with deformable image registration inadaptive radiotherapy’” [Med. Phys.39, 6531–6533 (2012)] Med. Phys. 40, 017102 (2013); 10.1118/1.4771963 Erratum: “Relationship between electron density and effective densities of body tissues for stopping, scattering,and nuclear interactions of proton and ion beams” [Med. Phys.39, 1016–1020 (2012)] Med. Phys. 40, 017202 (2013); 10.1118/1.4769415 Reply to “Comment on ‘Correspondence factor for Nucletron surface applicators’” [Med. Phys.39, 2947–2948(2012)] Med. Phys. 39, 2310 (2012); 10.1118/1.3694512 Gamma electron vertex imaging and application to beam range verification in proton therapy Med. Phys. 39, 1001 (2012); 10.1118/1.3662890

Two-Dimensional Prompt Gamma Measurement Simulation for In Vivo Dose Verification in Proton Therapy: A Monte Carlo Study

Abstract In proton therapy, accurate verification of in vivo dose distribution is necessary to ensure not only the safety of the patient but also the success of the treatment itself. It has been shown, both by Monte Carlo simulations and by limited experiments, that the proton beam range in a patient can be accurately determined by measuring the distribution of the prompt gammas generated from proton-induced nuclear interactions. In the present study, a two-dimensional (2-D) prompt gamma detection system incorporating a 51 (longitudinal) × 21 (lateral) detector array was designed and tested by Monte Carlo simulations using the MCNPX code. Additionally, the detection probability of the prompt gammas per primary proton was calculated for different proton energies. Despite the increase of the beam dispersion effect and background gammas with the increase of the proton energy, our simulation results clearly showed that it is possible to measure the 2-D distribution of prompt gammas up to 150 MeV using the 2-D prompt gamma detection system.

Development of Compton imaging system for nuclear material monitoring at pyroprocessing test-bed facility

ABSTRACT The Korea Atomic Energy Research Institute (KAERI) has constructed a test-bed facility, named PRIDE (PyRoprocess Integrated inactive DEmonstration), for demonstration of pyroprocessing technology. Even though the PRIDE facility utilizes depleted uranium, instead of actual spent fuel, as process material, it will play an important role not only from the process perspective, but also from the safeguards standpoint. In the present study, a Compton imaging system based on pixelated GAGG:Ce scintillation detectors was constructed and tested to determine its utility for accurate imaging of nuclear material locations and, thus, its applicability as a safeguards monitoring system at the PRIDE facility. In a lab-scale performance evaluation, when the dose rate induced by a 137Cs point-like source was ∼0.1 μSv/h, the source location was imaged within 5 min. The image resolutions were 22° and 7.6° for real-time monitoring using a back-projection algorithm and for near-real-time monitoring using a statistical iterative algorithm, respectively. The developed Compton imaging system was finally applied to low-enriched uranium and also to depleted uranium, which latter is the process material of the PRIDE facility, and it was indicated that the Compton imaging system can localize nuclear materials within a few minutes under conditions similar to those prevailing at the PRIDE facility. The results of this study show that the Compton imaging system, and Compton imaging technology in general, has a great potential for utilization as a nuclear material monitoring tool at the PRIDE facility.

Gamma electron vertex imaging for in-vivo beam-range measurement in proton therapy: Experimental results

Proton therapy, thanks to the dose characteristics of the Bragg peak, according to which most of the radiation energy is delivered at the end of the beam with a very high dose gradient at the distal edge, can deliver a highly conformal radiation dose to the treatment volume. Currently, however, the benefit of this high dose gradient is not fully utilized in clinical practice due mainly to the dose-distribution uncertainty in the beam direction (i.e., the uncertainty of the beam range in the patient). In this paper, we present an imaging system based on gamma electron vertex imaging (GEVI), which is suitable for high-energy (1–30 MeV) gammas, and test its performance for therapeutic proton beams. GEVI images prompt gamma vertices, which are closely correlated with the dose distribution at the distal edge, by converting prompt gammas to electrons via Compton scattering and then tracking the recoiled electrons. Our experimental results show that the GEVI system can image the 2D vertices of the prompt gammas and, thus, can be utilized for the measurement of proton-beam ranges in patients. We believe, indeed, that GEVI makes possible real-time monitoring of in-vivo proton-beam ranges, whose utility significantly improves treatment effectiveness and enhances patient safety. We also expect that the GEVI system will find applications in other fields (e.g., gamma-ray astronomy, nuclear engineering, and high-energy physics) requiring high-energy-gamma (1–30 MeV) imaging.